Mulching mowers are known which direct the grass clippings that have been severed by the cutting blade downwardly out of the cutting chamber to deposit such clippings in the standing grass remaining in the cut grass path. Various kinds of such mulching mowers are known. For example, mulching mowers are disclosed in U.S. Pat. Nos. 4,205,512 and 4,951,449 to Thorud, both of which are assigned to the assignee of this invention.
The mulching mowers shown in the Thorud patents have grass deflecting members or kickers within the cutting chamber to assist in the downward movement of the grass clippings. These kickers comprise angled grass deflecting surfaces that are fixed in each cutting chamber above the plane of the blade. The grass deflecting surfaces are shaped and positioned to intercept the grass clippings as they are being circulated inside the cutting chamber to redirect such clippings downwardly. The kickers are spaced apart around the circumference of the cutting chamber.
Other mulching mowers are known in which no kicker members are present in the cutting chamber. Instead, the cutting chamber and blade are specially shaped to effect mulching. For example, U.S. Pat. No. 3,085,386 to Slemmons discloses a mulching mower having a donut-shaped cutting chamber. A specially configured cutting blade is shaped to cause the grass clippings to be cut in a radial outer portion of the cutting chamber and to be circulated upwardly and inwardly inside the cutting chamber to eventually be driven downwardly out of the cutting chamber through a radial inner portion of the chamber.
The cutting blade shown in the Slemmons patent includes a radial outer tip portion having a cutting edge for severing the grass in the radial outer portion of the cutting chamber. An upwardly directed sail trails the cutting edge of the blade for standing the grass up and for causing a circumferential airflow within the housing which airflow circulates the grass clippings. An intermediate blade section is provided immediately adjacent the radial outer tip of the blade which intermediate section is twisted relative to the outer tip of the blade to be forwardly inclined. This "twisted" blade section allegedly provides a downdraft to help suck the grass clippings downwardly in the radial inner half of the cutting chamber to assist in depositing the clippings into the cut grass path. This "twisted" blade configuration has long been used in this type of donut-shaped housing for mulching. It is often referred to in the lawn mower art as a Bolens type mulcher.
While the mowers described above have been effective for mulching, they require either a specially manufactured housing or blade, as in the Bolens mulchers, or require that a number of kickers be fitted into, or manufactured as part of, the mower housing, as in the Thorud patents. The "twisted" Bolens mulching blade is effectively used only in the particular donut-shaped housing for which it is designed and cannot, therefore, be generally retrofit to mowers having a different housing configuration. Moreover, the "twisted" blade configuration is more difficult, and thus more expensive, to manufacture.
At any given time during their operation, mulching mowers have a large number of grass clippings which are confined inside the cutting chamber and are being circulated in a generally circumferential direction therein. The purpose of the mulching mower is to evacuate these clippings from the chamber by driving them downwardly into the cut grass path and hiding them there.
Applicant has observed that mulching mowers can be stalled when attempting to cut in difficult cutting conditions, such as when cutting particularly tallgrass, and to mulch the resulting clippings. The power requirements to effectively mulch in these conditions are considerable. As a practical matter, one observed characteristic of the use of such mowers in tall grass conditions is that they will stall or stop if the user attempts to travel through the grass too quickly. Accordingly, the user must mulch the grass quite slowly or by cutting the grass in narrow swaths which are narrower than the normal cutting width of the mower. This increases the amount of time required to cut the grass and is, consequently, a disadvantage.